The present invention relates to an all-optical wavelength converter used in an ultrahigh-speed wavelength division multiplexing optical communication system network and, more particularly, to an all-optical wavelength converter using a semiconductor optical amplifier and a polarization interferometer which are going to be used as crucial devices in an ultrahigh-speed wavelength division multiplexing optical communication system network.
A wavelength converter for converting a wavelength of transmitted signals to a wanted wavelength is used in the case of matching a wavelength of a transmission system to that of respective sub-net or node and is also used in the case of wavelength reuse.
A conventional wavelength converter using cross gain modulation (hereafter, referred as XGM) of a semiconductor amplifier is shown in FIG. 1.
In order to use XGM of a semiconductor amplifier, a signal light of wavelength .lambda.1 and a continuous wave laser of wavelength .lambda.2 should be inputted into the semiconductor amplifier at the same time, then the light of wavelength .lambda.2 undergoes a change by gain competition between two wavelengths and becomes a complementary signal that is fully inverted compared to the signal light.
The method mentioned above has an advantage of simplicity in structure, but it also has several problems. The fact that it always outputs complementary signals, bandwidth limitation by interband transition time(.about.ns) of electrons and decrease in extinction ratio by amplified spontaneous emission are the examples of such problems.